Wellbore pressure control is typically based on pre-drilling assumptions and data from offset wells. Actual conditions in earth formations (e.g., pore pressure, shear failure pressure, fracture pressure and in-situ stress) determined in real time as a well is being drilled have not, however, been taken into consideration in common wellbore pressure control systems. It would be advantageous if a wellbore pressure control system were capable of controlling wellbore pressure based on such real time geomechanics information.